>
>2 Wrote:
>
>I had written:
>>>But dipping the two capacitors on their own tells you *nothing* about
>>>their behavior in-circuit.
>>>
>>// The issue at hand is using two, paralleled capacitors as a DC
>>blocker. My position is one DC blocking cap with more current capability
>>is a better choice
>>
>Not unless the current capacity is more than two times greater than each
>of the two paralleled caps.
>
// Do two equal-capacitance paralleled caps have a resonance?
>>>However, you can make some real measurements using an MFJ or Autek SWR
>>>analyzer:
>>>* To look for a series resonance, connect the components in series with
>>>a 50 ohm resistor and sweep the frequency - SWR dips to 1 wherever the
>>>total reactance is very low compared with 50 ohms.
>>
>>// So Mr. Rauch was in error about the MFJ analyzer's dipper
>>disfunction?
>
>Since I don't know exactly what you mean, I wouldn't care to comment.
>
// Mr. Rauch stated that the dipmeter adapter does not work correctly.
>>>* To look for a parallel resonance, connect the components in parallel
>>>with a 50 ohm resistor and sweep the frequency - SWR dips to 1 wherever
>>>the total reactance is very high compared with 50 ohms.
>>>
>>// The hat-trick is finding an elusive zero-L 50-ohm resistor.
>>
>Not at all - any physically small carbon-film or metal-oxide resistor
>will have a low enough inductance for all but the most accurate
>measurements at HF.
>
// In my experiences 50, 57, and 58 Series doorknob caps have a
resonance at VHF or UHF. A 0.01uF disc ceramic cap resonates c. 10MHz.
>Most modern CF/MO resistors have a spiral element, but if you scrape off
>the paint, measure the diameter and length, and count the turns, you can
>estimate the inductance using the normal coil formula. You'll find that
>at low impedance levels the inductance is generally too small to matter
>below 30MHz.
>
// ... which is about as useful as teats on a boar.
>The inductance of these resistors only begins to matter at VHF. For even
>lower inductance you can switch to chip resistors, and they are good for
>accurate SWR and return loss measurements up to at least 1GHz.
>
>>>A network analyzer it isn't, but it does show what kind of resonances
>>>you have, and where they are.
>>>
>>// Dipmeters don't show where resonances are?
>
>Of course dipmeters show where resonances are - but that is all. They
>don't show what those resonances mean.
>
cheers, Ian
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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